static compression ratio is only part of the equation. You can use it as a minimum limit, such that if you have a 8:1 or 8.5:1 static compression ratio (simple volume of cylinder at top dead center vs bottom dead center) then unless the motor has some crazy efficiency and has high cylinder pressures at top rpm, you will most likely not need high octane gas. General rule of thumb I see is less than 9:1 compression ratio always run 87 octane gas.
On the other end of the spectrum, you can run around 11:1 compression which is usually associates itself with high octane gas (91/93 and higher). But... what kind of cam your running has a big impact. How long the intake stays open on the compression stroke relieves compression, and how much valve overlap also plays into things, which is the dynamic compression ratio and what really determines required fuel octane. And which is also why motors can run 10:1 to 11:1 CR and get by on 87 octane gas, or why some can and others must use 93 octane or better.
it's actually cylinder pressure you want to know for octane requirement. I thought i remember hearing or reading that for regular pump gasoline, and not sure if that means 87 octane or up to 93 octane is pump gas, that cylinder pressures should be < ~ 200psi. I think that was for a static measurement, as with a CR gauge cranking the motor with the starter. What cylinder pressures are at rpm I don't know. Run a CR gauge off a cylinder and run the motor at 3000-4000 rpm and find out for us